Aspects of the present invention relate to cooling systems for data centers.
A data center is generally defined as a room, or in some cases, an entire building or buildings, that houses numerous printed circuit (PC) board electronic systems arranged in a number of racks. Multiple racks are arranged into a row. The standard rack may be defined according to dimensions set by the Electronics Industry Association (EIA) for an enclosure: 78 in. (2 meters) wide, 24 in. (0.61 meter) wide and 30 in. (0.76 meter) deep.
Standard racks can be configured to house different combination of components including servers, networking equipment, and/or storage devices. In some cases, the components are embedded in a number of PC boards, ranging from about forty (40) boards, with future configuration of racks being designed to accommodate up to eighty (80) boards. The PC boards may include a number of sub-components, e.g., processors, micro-controllers, high-speed video cards, memories, and semi-conductor devices that dissipate relatively significant amounts of heat during the operation. For example, a typical PC board with multiple microprocessors may dissipate as much as 250 W of power. Consequently, a rack containing 40 PC boards of this type may dissipate approximately 10 KW of power.
Generally, the power used to remove heat generated by the components is equal to about 10 percent of the power used for their operation. However, the power required to remove the heat dissipated by the same components configured into a multiple racks in a data center is generally greater. In many cases, the cooling load required in the data center corresponds to the power drawn by the servers and can be equal to about 50 percent of the power used for their operation. For example, in vapor-compression driven cooling systems, the power drawn by compressors alone can be as high as 30% of the power consumed by servers in a data center.
The difference in required power for dissipating the various heat loads between racks and data centers can be attributed to the additional thermodynamic work needed in the data center to cool the air. For example, racks typically use fans to move cooling fluid (e.g., air) across the heat dissipating components for cooling. Data centers in turn often implement reverse power cycles to cool heated return air from the racks. This additional work associated with moving the cooling fluid through the data center and cooling equipment consumed large amounts of energy and makes cooling large data centers difficult.
In practice, conventional data centers are cooled using one or more Computer Room Air Conditioning units, or CRAC units. The typical compressor unit in the CRAC is powered using a minimum of about thirty (30) percent of the power required to sufficiently cool the data centers. The other components, e.g., condensers, air movers (fans), etc., typically require an additional twenty (20) percent of the required cooling capacity.
As an example, a high density data center with 100 racks, each rack having a maximum power dissipation of 10 KW, generally requires 1 MW of cooling capacity. Consequently, air conditioning units having the capacity to remove 1 MW of heat generally require a minimum of 300 KW to drive the input compressor power and additional power to drive the air moving devices (e.g., fans and blowers).
Conventional data center CRAC units do not vary their cooling fluid output based on the distributed needs of the data center. Instead, these CRAC units generally operate at or near a maximum compressor power even when the heat load is reduced inside the data center. This substantially continuous operation of the CRAC units is generally designed to operate according to a worst-case scenario. That is, cooling fluid is supplied to the components at around 100 percent of the estimated cooling requirement. Often, these conventional cooling systems attempt to cool components even though they may not be operating at a level that exceeds a predetermined temperature range. Moreover, conventional systems generally measure ambient temperature at sensors located at the CRAC units, and not at the locations in the data center where the racks and heat-producing equipment is located. For at least these reasons, conventional cooling systems generally incur greater amounts of operating expenses than may be necessary to sufficiently cool the heat-generating components contained in the racks of data centers.